1. Field of the Invention
This invention relates to hard disk drives. More particularly, this invention relates to a pivot assembly for rotating a head stack assembly of the hard disk drive.
2. Description of the Prior Art and Related Information
A huge market exists for hard disk drives for mass-market host computer systems such as servers, desktop computers, and laptop computers. To be competitive in this market, a hard disk drive must be relatively inexpensive, and must accordingly embody a design that is adapted for low-cost mass production. In addition, it must provide substantial capacity, rapid access to data, and reliable performance. Numerous manufacturers compete in this huge market and collectively conduct substantial research and development, at great annual cost, to design and develop innovative hard disk drives to meet increasingly demanding customer requirements.
Each of numerous contemporary mass-market hard disk drive models provides relatively large capacity, often in excess of 1 gigabyte per drive. Nevertheless, there exists substantial competitive pressure to develop mass-market hard disk drives that have even higher capacities and that provide rapid access. Another requirement to be competitive in this market is that the hard disk drive must conform to a selected standard exterior size and shape often referred to as a "form factor." Generally, capacity is desirably increased without increasing the form factor or the form factor is reduced without decreasing capacity.
Satisfying these competing constraints of low-cost, small size, high capacity, and rapid access requires innovation in each of numerous components and methods of assembly including methods of assembly of various components into certain subassemblies. Typically, the main assemblies of a hard disk drive are a head disk assembly and a printed circuit board assembly.
The head disk assembly includes an enclosure including a base and a cover, at least one disk having at least one recording surface, a spindle motor for causing each disk to rotate, and an actuator arrangement. The printed circuit board assembly includes circuitry for processing signals and controlling operations.
Actuator arrangements can be characterized as either linear or rotary; substantially every contemporary cost-competitive small form factor drive employs a rotary actuator arrangement.
The rotary actuator arrangement is a collection of elements of the head disk assembly; the collection typically includes certain prefabricated subassemblies and certain components that are incorporated into the head disk assembly. The prefabricated assemblies include a pivot bearing cartridge and, in some cases, a prefabricated head stack assembly. Other components of the rotary actuator arrangement are permanent magnets and an arrangement for supporting the magnets to produce a magnetic field for a voice coil motor. The prefabricated head stack assembly includes a coil forming another part of the voice coil motor. The prefabricated head stack assembly also includes an actuator body having a bore through it, and a plurality of arms projecting parallel to each other and perpendicular to the axis of the bore. The prefabricated head stack assembly also includes head gimbal assemblies that are supported by the arms. Each head gimbal assembly includes a load beam and a head supported by the load beam.
The pivot bearing cartridge typically includes an outer shell, longitudinally spaced-apart ball bearings and an inner shaft with the inner shaft being attached to the base to define an axis of rotation for the rotary actuator. While the pivot bearing cartridge has worked well for its intended purpose, it is relatively expensive due to the cost of the ball bearings. Accordingly, research and development efforts have been expended in efforts to provide a lower-cost alternative to the pivot bearing cartridge.
U.S. Pat. No. 5,355,268 to Schulze ("Schulze") discloses one such lower cost alternative in which a pivot assembly uses knife edge pivot technology. Prior Art FIG. 1 of this application is generally representative of each of the embodiments disclosed in the patent in which the pivot assembly is configured such that a knife edge faces in a direction in line with the longitudinal axis of an actuator arm. With reference to Prior Art FIG. 1, a portion of a head stack assembly and a pivot assembly 117 installed in its bore 102 are shown. The head stack assembly includes an actuator body 100 defining bore 102 and an actuator arm 106. Actuator arm 106 defines a longitudinal axis 108. When the head stack assembly is installed in a disk drive, actuator arm 106 moves in a direction which is primarily radial relative to a recording surface of a disk (not shown). The radial movement of the actuator arm includes movement in an off-track direction 109 relative to a selected track on the recording surface; based on this we define the off-track direction as being perpendicular to longitudinal axis 108.
Pivot assembly 117 includes a stationary member 110 having a recessed portion 104 and a rotatable member 112 attached to a surface of bore 102. Rotatable member 112 includes a projecting member 114 having a knife edge 116. Recessed portion 104 receives knife edge 116 such that rotatable member 112 and hence, the actuator arm, rotates partially relative to the stationary member. In the prior art, knife edge 116 faces in a direction in line with the longitudinal axis 108. In such a configuration, knife edge 116 is in shear and bending relative to recessed portion 104 as actuator arm 106 moves in off-track direction 109 such that the stiffness in the off-track direction is relatively low. Such a low stiffness leads to relatively large amplitude resonance(s) of a head (not shown) coupled to actuator arm 106 at frequencies which are detrimental to the performance of most present day servo systems.
With reference to FIG. 5, a Prior Art plot 500 represents the magnitude of vibrations of the head as a function of frequency. As shown, the plot includes a peak 502 at about 2.7 kHz which has a magnitude of 25 dB. The magnitude is measured relative to an imaginary line 700 which represents an ideal situation in which no vibrations occur. In most present day hard disk drives, the presence of any significant resonances occurring between the frequencies of 1 to 4 kHz may result in instability of the servo system and/or writing and reading off-track. As a result, any significant resonances (i.e., those whose magnitude exceeds about 15 dB relative to imaginary line 700) of the head are preferably located at a resonant frequency of 4 kHz or higher.